Cold cathode display device



23, 1960 A. M. SKELLETT cow CATHODE DISPLAY DEVICE Filed Sept. 19, 1958INVENTOR Azaser Ail/44: rr

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United States Patent 6 2,926,286 I COLD CATHODE DISPLAY DEVICE Albert M.Skellett, Madison, N.J., amigior to Tang-Sol Electric Inc., acorporation of Delaware Application September 19, 1958, Serial No.762,042

' Claims. or. 315169) v The present invention relates to display devicesor panls such as may be used with television receivers or the like andcomprises a novel device which yields a bright image, has a long usefullife and is relatively economical to manufacture and to operate.

Two general types of display devices are well known in the art. Thecathode ray tube in which the location of a luminous spot on thephosphor screen is varied by control of the deflection of an electronbeam represents one known type of display device. An electroluminescentpanel in which the location of thelurninescent spot on the panel isvaried by control of the application'of alternating potentials acrossdifferent pairs of conductors of arrays positioned on'opposite sides ofa layer of electroluminescent phosphor material represents the otherknown type of display device. The device of the present inventiondifiers radically from the' above mentioned prior art'devices althoughemploying some of the features of each. Like the cathode ray tube, thenew device is evacuated and employs a phosphor screen which luminesceswhen bombarded by electrons. The source of electrons is a cold cathodeof the type which, once electron emission is initiated, provides aself-sustaining copious flow of electrons. The cathode covers an areasubstantially equal to that of the phosphor screen. Between the cathodeand phosphor screen is a grid which when maintained at a potential abovethat of the cathode maintains electron emission. Two arrays of mutuallyperpendicular parallel conductors, comparable physically to thoseemployed in electroluminescent devices, are positioned between the gridand screen and control the location of the luminous spot in response toselective application of control potentials thereto. The conductors ofthese arrays correspond in function to control and screen grids of anelectronic amplifier.

For a better understanding of the invention and of the advantagesthereof reference may be had to the accompanying drawing of which:

Fig. 1 is a plan view, partly broken away, of a display device embodyingthe invention, the electrical connections and suitable associatedcircuit being also shown;

Fig. 2 is a fragmentary vertical sectional View taken on the line 22 ofFig. 1; and

Fig. 3 is a graph explanatory of the operation of the device of Fig. 1.

The new display device includes .a front panel 2 of glass or other lighttransmitting material and a rear panel 4 which may be of metal or ofglass having a conductive coating applied to the inner surface thereof.The space between the panels 2 and 4 is evacuated and their peripheriesare hermetically joined, as shown in Fig. 2, by flanges 6. On the innersurface of the panel 4 is a coating '8 of a material adapted to. emitelectrons. The coating, which serves as a cold cathode, is preferablymagnesium oxide in the form of a uniform distribution of microscopicsponge-like structures. Such a coating, once electron emission isinitiated, will emit a copious stream of electrons so long as anelectrode positive with respect 2,926,286 Patented l 'eln 21 5, '2

to the coating is provided for collection of the emitted electrons.Positioned within the enclosure provided by the panels 2 and 4 andadjacent the cathode coating 8 is a grid 10 for sustaining electronemission from thecath ode. Two arrays, 12 and 14, of mutuallyperpendicular conductors are positioned between the grid loandthe panel2. In the particular embodiment of the invention illustrated in thedrawing the conductors of array 12 are vertically disposed and theconductors of array 14 are horizontally disposed. On the inner surfaceof panel 2 is a transparent conductive film 16 of stannic oxide or thelike and on the film 16 is a layer 18 of cathodo-luminescent phosphormaterial such as a mixture of suitably activated zinc and cadmiumsulfides. In order to initiate electronemission from the cathode 8, asource of ultraviolet radiation, such as an electroluminescent device 20is provided within the enclosure. The starter 20 may ice ' be, andpreferably is, of the type disclosed in applicants copendingapplication, Serial No. 745,149, filed June 27, 1958, to which referencemay be had for a detailed description thereof. Briefly, the startercomprises a glass or quartz sheet 22 having a transparent conductivefilm 24 thereon, a layer 26 of dielectric material in which anelectroluminescentphosphor is embedded and an outer conductive film 28,the two conductive films being con nected to a. suitable external source30 of alternating current by leads 32 which are sealed through theflange .6 of the device. Alternatively, if the wall member 4.is of glassor other transparent material, the starter 20 maybe omitted and electronemission initiated by external means, for example by excitation withhigh frequency energy from :1 Tesla coil.

Before discussing circuit connections for the display device, a briefexplanation will be given of the function of the elements so faridentified. The coating 8, in conjunction with the sustaining grid 10,corresponds to a cathode of a vacuum tube, the conductive film 16corresponds to the anode of a vacuum tube and arrays 12 and 14correspond, respectively, to control and screen grids of such a tube. Ifin each array all conductors but one are grounded, then the potentialsapplied to the two ungrounded conductors will control the electronstream to that small portion of the film 16 which is aligned with thepoint of cross-over of such two conductors. The luminosity of thephosphor material on such small portion of film 16 will also depend uponthe voltages impressed on the two conductors. More specifically, if thefilm 16 is maintained at 350 volts above cathode potential and if theone conductor of array 14-under consideration is maintained at 150volts, then the current tofilm 16 will vary with the voltage applied tothe conductor of array 12 in accordance with the curve of v Fig. 3wherein anode current is represented as a function.

doctors of array 14 should be synchronized withfithe vertical sweepfrequency and the applied voltages to the vertical conductors of array12 should be controlled by the video signal and the sequentialapplication thereof synchronized with the horizontal sweep frequency-ofthe receiver. Such a circuitarrangement is diagrammatically shown inFig. 1.

As shown in Fig. 1 the conductors of array 12 are brought out throughexternal leads 12a to terminals 12b adapted to be sequentially engagedby a rotating switch arm 34 the rate of rotation of which issynchronized with the horizontal sweep voltage. A source of voltagemodulated by the video signal, illustrated diagrammatically at 36, isconnected to the arm 34 to sequentially impress control voltages uponthe conductors 12.' To provide effective grounding of the conductors ofarray 12 when no controlling voltage is impressed thereon, the end ofeach remote from a terminal 12b is connected to ground through a highresistor 38 of the order of 1 megohm. The horizontal conductors of array14 are similarly connected by means of conductors 14a to terminals 14!)adapted to be sequentially engaged by a rotating arm 40. The other endsof the conductors of array 14 are connected to ground through resistors42, the rate of rotation of arm at being synchronized with the verticalsweep frequency. A source of direct current ener-g', indicated as abattery 42', has its negative terminai grounded and its positiveterminal connected to the conductive film 16 of the display device by alead 44. A point of intermediate voltage of the battery 42 is connectedto the arm 4t? and to the grid electrode Panel 4, if of metal, or theconductive film thereon if of glass, is grounded as indicated at 46.

With the above described arrangement once electron emission is initiatedfrom the cathode 8 the emission is sustained by the potential applied togrid 10. During rotation of the arms 34 and 4t) sequential small areasof the phosphor layer 18 will luminesce under control of the videosignal as heretofore described.

Any known means may be provided for properly synchronizingthe rotationof arms 34 and 41') with the horizontal and vertical sweep frequencies.In the particular circuit of Fig. 1, one suitable type of synchronizingmeans is disclosed as comprising a pivoted pawl 48 which is'biased by aspring 50 into engagement with stop 52 in which position the end of thepawl arrests movement of the rotating arm. A solenoid 54 connected tothe horizontal sweep generator, through a rectifier 56, in the case ofthe control of arm 34, attracts the pawl 48 during the fly back periodthus synchronizing rotation of the arm 34 with the horizontal sweepfrequency, the arm 34 being driven at slightly above synchronousfrequency through a friction clutch or the like. In the case of the arm-46 the solenoid 54 will be energized during the fiy back period of thevertical sweep and the arm 49 will be rotated at a rate slightly abovethe vertical frequency. Details of the synchronizing means arenot'believed necessary as instrumentalities for properly synchronizingthe rotation of the arms 34 and 40 arewell lgnown in the art. Forexample, a. single revolution clutchcould be employed instead of theparticular construction illustrated.

It will be understood that for purposes of clarity in the drawingrelatively few conductors have been shown in each of the arrays 12 and14. Obviously for television I purposes a greater number of conductorswould be ernceivers obviously the display device could be used forradaror other display purposes.

The following is claimed: 1. A display device comprising two generallyparallel wall members hermetically sealed together about theirperipheries to form a single evacuated envelope, one of said wallmembers being of transparent electrical insulating material and theother of said wall members being electrically conductive at least on itsinner surface, a porous coating on the inner surface of said lastmentioned wail member of a cold cathode material capable, once electronemission has been initiated, of self-sustained electron emission, a gridelectrode within the envelope spaced from the cold cathode coating, afirst array of parallel conductors within the envelope spaced from saidgrid electrode, a second array of parallel conductors within theenvelope spaced from said first array and with the conductors thereofangularly disposed with respect to the conductors of the first array, atransparent conductive film on the inner surface of said transparentwall memher and a phosphor layer on said conductive film, said grid whenmaintained at a potential above that of the cathode coating serving tosustain electron emission, said film, when maintained at a potentialabove that of said grid serving to receive electrons from said cathodeunder control of selective application of control potentials toconductors of said arrays, said phosphor layer emitting light whenbombarded by electrons traveling to said film.

2. The display device according to claim 1 including means within theenvelope for initiating electron emission. from saidv cathode coating,said means comprising an.

3. The displaydevice according to claim 1 wherein one end of eachconductor of each array is connected,

externally of the envelope, to ground through a high resister and theother ends of the conductors-of one array are connected to one set ofterminals and the other endsof the conductors of the other array areconnected to a second set of terminals, and means for sequentiallyapplying control voltages to said sets of terminals.

4. The display device according to claim 1 wherein said cathode coating.is magnesium oxide in the form of microscopic sponge-like structures.

5. A display device comprising two generally parallel wall membershermetically sealed together about their peripheries to form anevacuated envelope, one of said wall members being of transparentelectrical insulating material and the other of said wall membershaving. an inner conductive surface, a coating on said inner surfaceofsaid last mentioned wall member of magnesium oxide in the form ofmicroscopic sponge-like structures, a grid electrode within the envelopegenerally parallel to and spaced from said coating, a first array ofparallel conductors within the envelope spaced from said grid electrode,a second array of parallel conductors within the envelope spaced fromsaid first array and with the conductors thereof perpendicularlydisposed with respect to of said arrays to control the location on saidphosphor layer of bombardment by electrons emitted from said coating.

References Cited in the file of this patent UNIT ED STATES PATENTSOk'olicsanyi Mar. 9; 1943 Marks Feb. 23, 1954

